1. Field of the Invention
The present invention relates to a color-purity measuring method for a color cathode ray tube, and a color-purity measuring apparatus.
2. Description of the Prior Art
In general, electron beams corresponding to each of red, green, and blue colors are emitted from an electron gun toward a screen of a color cathode ray tube for causing an image to appear on the screen. Respective optical axes are passed through an aperture grill. It is thereby arranged that the respective electron beams provided on the screen are incident upon red, green, and blue phosphor stripes (or dots) corresponding to these electron beams.
Conventionally, for measuring whether the electron beams corresponding to the red, green, and blue phosphor stripes (or dots), corresponding to these electron beams, provided on the screen are each being correctly incident upon it, the following measures are taken. Namely, an adjusting coil that vertically or horizontally applies a magnetic field to the color cathode ray tube is mounted to a neck portion of the color cathode ray tube. The amount of electric current passed through the adjusting coil and the movement distance of the electron beam, varying depending upon the magnetic field generated due thereto, are visually measured using a microscope.
However, conventionally, since the movement distance of the electron beam in a unit of micron was visually measured, this became a large factor in causing the generation of measurement errors.
Also, there was the inconvenience that a very much greater length of time was needed for measurement as the measured points increased. For example, in a color cathode ray tube, there is a method wherein the color purity at each of 117 points in all of vertical 9 pointsxc3x97horizontal 13 points of the screen is corrected based on the measurement data. It is thereby intended to improve the color purity. However, in this case, only a center point alone was measured, and, regarding each of the other points, the value of the relevant color purity was corrected by substituting data corresponding to the center point.
In that case, the amount of movement of the electron beam that originally differs between a zone including the center and its neighborhood and a zone including a corner and its neighborhood was corrected using the same values. For this reason, there was the inconvenience that such correction was unable to become an excellent correction of the color purity.
The present invention has been made in view of the above-described problematical points and has an object to enable easy measurement of the amount of color purity at each of many measured points.
A color-purity measuring method according to an example of the present invention is arranged as follows. An adjusting coil is provided at a neck portion of a color cathode ray tube, and there is provided a color image pickup means for photographing the screen of the color cathode ray tube. And, there is provided input means for inputting to the color cathode ray tube a monochrome signal of any one of red, green, and blue color signals. An image pickup signal obtained from the color image pickup means is decomposed into red, green, and blue color signal components while causing an electric current made to flow through the adjusting coil to vary thereby to measure the luminance of each of them. Then, the electric-current value difference between a first electric current value made to flow through the adjusting coil at which the intensity of any one of the red, green, and blue color signal components becomes maximum and a second electric current value made to flow through the adjusting coil at which the intensity of another one of the red, green, and blue color signal components becomes maximum is determined. The amount of movement of an electron beam with respect to a unit value of electric current for the adjusting coil according to the electric current value difference and the location distance between light-emitting regions of the red, green, and blue colors on the color cathode ray tube is determined. Thereby, the amount of color-purity at a relevant measured point is determined according to the amount of movement of an electron beam with respect to a unit value of electric current for the adjusting coil and the value of the electric current corresponding to the intensity peak of the monochrome signal of any said one color signal.
Also, a color-purity measuring apparatus according to an example of the present invention is arranged as follows. It includes an adjusting coil that is mounted at a neck portion of a color cathode ray tube, color image pickup means that photographs a screen of the color cathode ray tube, input means that inputs a monochrome signal of any one of red, green, and blue color signals to the color cathode ray tube, memory means that decomposes a color video signal obtained at the color image pickup means into red, green, and blue color signals and stores these signals therein, variable current supply means that supplies a variable electric current to the adjusting coil, and calculation means that determines an electric-current value difference between a first electric current value made to flow through the adjusting coil at which the intensity of any one of the red, green, and blue color signal obtained in the memory means becomes maximum and a second electric current value made to flow through the adjusting coil at which the intensity of another one of the red, green, and blue color signals becomes maximum, an amount of movement of an electron beam with respect to a unit value of electric current for the adjusting coil according to the electric current value difference and the location distance between light-emitting regions of the red, green, and blue colors on the color cathode ray tube and an amount of color-purity at a relevant measured point according to the amount of movement of an electron beam with respect to a unit value of electric current for the adjusting coil.
According to the above-described present invention, when determining an amount of color purity of, for example, a green color at each of the respective measured points on a color cathode ray tube, a green color signal is input to the color cathode ray tube. Thereby, the screen is set to a green-monochromatic raster one, and this screen is photographed by the color image pickup means. At this time, with respect to this color cathode ray tube, the adjusting coil is mounted at the neck portion of the tube so as to apply a magnetic field, for example, vertically to it. A variable electric current is made to flow through that adjusting coil. Then, the electric-current value difference between a first electric current value made to flow through the adjusting coil at which the intensity of any one of the red, green, and blue color signals at the relevant measured point becomes maximum and a second electric current value made to flow through the adjusting coil at which the intensity of another one of the red, green, and blue color signals becomes maximum is determined. Thereby, the amount of movement of an electron beam with respect to a unit value of electric current for the adjusting coil according to the electric current value difference and the location distance between light-emitting regions of the red, green, and blue colors on the color cathode ray tube is determined. Then, the electric current value made to flow through the adjusting coil at which the intensity value of the green color at each of the respective measured points becomes maximum is determined. This electric current value is multiplied by the amount of movement of the electron beam with respect to that unit value of electric current. By doing so, it is possible to determine the amount of color purity at each of the measured points.
According to the present invention, similarly, it is possible with respect to every point of the screen of the color cathode ray tube photographed by the color image pickup means, to easily measure the amount of color purity of each of the red, green, and blue colors.